<!DOCTYPE html><html lang="zh-Hans"><head><meta charset="UTF-8"><meta http-equiv="X-UA-Compatible" content="IE=edge"><meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1"><meta name="description" content="KVO原理及实现"><meta name="keywords" content=""><meta name="author" content="kyren"><meta name="copyright" content="kyren"><title>KVO原理及实现 | Kyren's Blog</title><link rel="shortcut icon" href="/melody-favicon.ico"><link rel="stylesheet" href="/css/index.css?version=1.9.0"><link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/font-awesome@latest/css/font-awesome.min.css?version=1.9.0"><meta name="format-detection" content="telephone=no"><meta http-equiv="x-dns-prefetch-control" content="on"><link rel="dns-prefetch" href="https://cdn.jsdelivr.net"><link rel="dns-prefetch" href="https://hm.baidu.com"><script>var _hmt = _hmt || [];
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<p>Person.h</p>
<figure class="highlight objectivec"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">#import <span class="string">&lt;Foundation/Foundation.h&gt;</span></span></span><br><span class="line"><span class="meta">#import <span class="string">&lt;UIKit/UIKit.h&gt;</span></span></span><br><span class="line"></span><br><span class="line"><span class="class"><span class="keyword">@interface</span> <span class="title">Person</span> : <span class="title">NSObject</span></span></span><br><span class="line"></span><br><span class="line"><span class="keyword">@property</span> (<span class="keyword">nonatomic</span>,<span class="keyword">copy</span>)    <span class="built_in">NSString</span> *userName;</span><br><span class="line"><span class="keyword">@property</span> (<span class="keyword">nonatomic</span>,<span class="keyword">assign</span>)  <span class="built_in">NSInteger</span> age;</span><br><span class="line"><span class="keyword">@property</span> (<span class="keyword">nonatomic</span>,<span class="keyword">assign</span>)  <span class="built_in">CGFloat</span> height;</span><br><span class="line"></span><br><span class="line"><span class="comment">//手动触发KVO</span></span><br><span class="line">-(<span class="type">void</span>)manualTriggerKVO;</span><br><span class="line"></span><br><span class="line"><span class="keyword">@end</span></span><br></pre></td></tr></table></figure>

<p>Person.m</p>
<figure class="highlight objectivec"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">#import <span class="string">&quot;Person.h&quot;</span></span></span><br><span class="line"><span class="meta">#import <span class="string">&lt;objc/runtime.h&gt;</span></span></span><br><span class="line"></span><br><span class="line"></span><br><span class="line"><span class="class"><span class="keyword">@implementation</span> <span class="title">Person</span></span></span><br><span class="line"></span><br><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> *  如果重写，这两个方法，kvo就失效了。</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"><span class="comment">//- (void)willChangeValueForKey:(NSString *)key&#123;</span></span><br><span class="line"><span class="comment">//    NSLog(@&quot;willChangeValueForKey&quot;);</span></span><br><span class="line"><span class="comment">//&#125;</span></span><br><span class="line"></span><br><span class="line"><span class="comment">//- (void)didChangeValueForKey:(NSString *)key&#123;</span></span><br><span class="line"><span class="comment">//    NSLog(@&quot;didChangeValueForKey&quot;);</span></span><br><span class="line"><span class="comment">//&#125;</span></span><br><span class="line"></span><br><span class="line">-(<span class="type">void</span>)manualTriggerKVO</span><br><span class="line">&#123;</span><br><span class="line">    <span class="comment">//“手动触发userName的KVO”，必写。</span></span><br><span class="line">    [<span class="keyword">self</span> willChangeValueForKey:<span class="string">@&quot;userName&quot;</span>];</span><br><span class="line"></span><br><span class="line">    <span class="comment">// “手动触发userName的KVO”，必写。</span></span><br><span class="line">    [<span class="keyword">self</span> didChangeValueForKey:<span class="string">@&quot;userName&quot;</span>];</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"><span class="comment">//options属性改变change的值，这个是观察者要实现的方法。</span></span><br><span class="line">- (<span class="type">void</span>)observeValueForKeyPath:(<span class="built_in">NSString</span> *)keyPath ofObject:(<span class="type">id</span>)object change:(<span class="built_in">NSDictionary</span>&lt;<span class="built_in">NSString</span> *,<span class="type">id</span>&gt; *)change context:(<span class="type">void</span> *)context&#123;</span><br><span class="line">    <span class="keyword">if</span> ([keyPath isEqualToString:<span class="string">@&quot;age&quot;</span>]) &#123;</span><br><span class="line">        <span class="built_in">NSLog</span>(<span class="string">@&quot;%@:%@&quot;</span>,<span class="keyword">self</span>.class,change);</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"><span class="keyword">@end</span></span><br></pre></td></tr></table></figure>



<figure class="highlight objectivec"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br><span class="line">56</span><br><span class="line">57</span><br><span class="line">58</span><br><span class="line">59</span><br><span class="line">60</span><br><span class="line">61</span><br><span class="line">62</span><br><span class="line">63</span><br><span class="line">64</span><br><span class="line">65</span><br><span class="line">66</span><br><span class="line">67</span><br><span class="line">68</span><br><span class="line">69</span><br><span class="line">70</span><br><span class="line">71</span><br><span class="line">72</span><br><span class="line">73</span><br><span class="line">74</span><br><span class="line">75</span><br><span class="line">76</span><br><span class="line">77</span><br><span class="line">78</span><br><span class="line">79</span><br><span class="line">80</span><br><span class="line">81</span><br><span class="line">82</span><br><span class="line">83</span><br><span class="line">84</span><br><span class="line">85</span><br><span class="line">86</span><br></pre></td><td class="code"><pre><span class="line">- (<span class="type">void</span>)viewDidLoad &#123;</span><br><span class="line">    [<span class="variable language_">super</span> viewDidLoad];</span><br><span class="line">    <span class="comment">// Do any additional setup after loading the view from its nib.</span></span><br><span class="line">    Person* one = [Person new];</span><br><span class="line">    Person* two = [Person new];</span><br><span class="line">    Person* three = [Person new];</span><br><span class="line"></span><br><span class="line">    printf(<span class="string">&quot;注册观察者之前\n&quot;</span>);</span><br><span class="line">    PrintDescription(<span class="string">@&quot;one&quot;</span>,one);</span><br><span class="line">    PrintDescription(<span class="string">@&quot;two&quot;</span>,two);</span><br><span class="line">    PrintDescription(<span class="string">@&quot;three&quot;</span>,three);</span><br><span class="line">    PrintMethodImp(<span class="string">@&quot;one&quot;</span>,one, <span class="keyword">@selector</span>(setUserName:));</span><br><span class="line">    PrintMethodImp(<span class="string">@&quot;two&quot;</span>,two, <span class="keyword">@selector</span>(setUserName:));</span><br><span class="line">    PrintMethodImp(<span class="string">@&quot;three&quot;</span>,three, <span class="keyword">@selector</span>(setUserName:));</span><br><span class="line"></span><br><span class="line">    [one addObserver:one forKeyPath:<span class="string">@&quot;age&quot;</span></span><br><span class="line">             options:<span class="built_in">NSKeyValueObservingOptionNew</span></span><br><span class="line">             context:<span class="literal">nil</span>];</span><br><span class="line">    [two addObserver:two forKeyPath:<span class="string">@&quot;height&quot;</span></span><br><span class="line">             options:<span class="built_in">NSKeyValueObservingOptionNew</span></span><br><span class="line">             context:<span class="literal">nil</span>];</span><br><span class="line"></span><br><span class="line">    printf(<span class="string">&quot;注册观察者之后\n&quot;</span>);</span><br><span class="line">    Class cls=  object_getClass(one);</span><br><span class="line">    <span class="built_in">NSLog</span>(<span class="string">@&quot;\n\t父类：%@&quot;</span>,cls.superclass);</span><br><span class="line"></span><br><span class="line">    PrintDescription(<span class="string">@&quot;one&quot;</span>,one);</span><br><span class="line">    PrintDescription(<span class="string">@&quot;two&quot;</span>,two);</span><br><span class="line">    PrintDescription(<span class="string">@&quot;three&quot;</span>,three);</span><br><span class="line">    PrintMethodImp(<span class="string">@&quot;one&quot;</span>,one, <span class="keyword">@selector</span>(setAge:));</span><br><span class="line">    PrintMethodImp(<span class="string">@&quot;two&quot;</span>,two, <span class="keyword">@selector</span>(setAge:));</span><br><span class="line">    PrintMethodImp(<span class="string">@&quot;three&quot;</span>,three, <span class="keyword">@selector</span>(setAge:));</span><br><span class="line"></span><br><span class="line">    one.age=<span class="number">18</span>;</span><br><span class="line">    two.age=<span class="number">25</span>;</span><br><span class="line">    three.age=<span class="number">43</span>;</span><br><span class="line">    printf(<span class="string">&quot;赋值观察者之后\n&quot;</span>);</span><br><span class="line">    PrintDescription(<span class="string">@&quot;one&quot;</span>,one);</span><br><span class="line">    PrintDescription(<span class="string">@&quot;two&quot;</span>,two);</span><br><span class="line">    PrintDescription(<span class="string">@&quot;three&quot;</span>,three);</span><br><span class="line">    PrintMethodImp(<span class="string">@&quot;one&quot;</span>,one, <span class="keyword">@selector</span>(setAge:));</span><br><span class="line">    PrintMethodImp(<span class="string">@&quot;two&quot;</span>,two, <span class="keyword">@selector</span>(setAge:));</span><br><span class="line">    PrintMethodImp(<span class="string">@&quot;three&quot;</span>,three, <span class="keyword">@selector</span>(setAge:));</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"><span class="meta">#<span class="keyword">pragma</span> mark--打印函数</span></span><br><span class="line"><span class="comment">/** 获取类的方法列表*/</span></span><br><span class="line"><span class="keyword">static</span> <span class="keyword">inline</span> <span class="built_in">NSArray</span> *classMethodList(Class aclass) &#123;</span><br><span class="line">    <span class="built_in">NSMutableArray</span>* array = [<span class="built_in">NSMutableArray</span> array];</span><br><span class="line">    <span class="type">unsigned</span> <span class="type">int</span> count = <span class="number">0</span>;</span><br><span class="line">    Method* methodList = class_copyMethodList(aclass, &amp;count);</span><br><span class="line">    <span class="keyword">for</span>(<span class="type">int</span> i = <span class="number">0</span>; i &lt; count; ++i) &#123;</span><br><span class="line">        SEL sel = method_getName(*(methodList+i));</span><br><span class="line">        [array addObject:<span class="built_in">NSStringFromSelector</span>(sel)];</span><br><span class="line">    &#125;</span><br><span class="line">    free(methodList);</span><br><span class="line">    <span class="keyword">return</span> array;</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"></span><br><span class="line"><span class="comment">/** 打印对象的信息*/</span></span><br><span class="line"><span class="keyword">static</span> <span class="keyword">inline</span> <span class="built_in">NSString</span> *PrintDescription(<span class="built_in">NSString</span> *name,<span class="type">id</span> obj) &#123;</span><br><span class="line">    <span class="built_in">NSString</span>* string = [<span class="built_in">NSString</span> stringWithFormat:<span class="string">@&quot;\t%@:%@\n\t表面的类: %@\n\t真实类型: %@\n\t方法列表: %@\n\t方法列表2: %@\n&quot;</span>,</span><br><span class="line">                        name,</span><br><span class="line">                        obj,</span><br><span class="line">                        [obj <span class="keyword">class</span>],</span><br><span class="line">                        object_getClass(obj),</span><br><span class="line">                        [classMethodList(object_getClass(obj)) componentsJoinedByString:<span class="string">@&quot;,&quot;</span>],</span><br><span class="line">                        [classMethodList([obj <span class="keyword">class</span>]) componentsJoinedByString:<span class="string">@&quot;,&quot;</span>]</span><br><span class="line">                        ];</span><br><span class="line"></span><br><span class="line">    printf(<span class="string">&quot;%s\n&quot;</span>, [string UTF8String]);</span><br><span class="line">    <span class="keyword">return</span> string;</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"><span class="comment">/** 打印方法方法实现指针*/</span></span><br><span class="line"><span class="keyword">static</span> <span class="type">void</span> PrintMethodImp(<span class="built_in">NSString</span> *name,<span class="type">id</span> cls,SEL  sel)</span><br><span class="line">&#123;</span><br><span class="line">    IMP imp1 =class_getMethodImplementation([cls <span class="keyword">class</span>],sel);</span><br><span class="line">    IMP imp11 =class_getMethodImplementation(object_getClass(cls),sel);</span><br><span class="line">    <span class="built_in">NSString</span> *selName=<span class="built_in">NSStringFromSelector</span>(sel);</span><br><span class="line">    printf(<span class="string">&quot;%s方法名%s：Class=%p subClass:%p\n&quot;</span>,[name  UTF8String],[selName  UTF8String],imp1,imp11);</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<p>打印信息如下：</p>
<figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br><span class="line">56</span><br><span class="line">57</span><br><span class="line">58</span><br><span class="line">59</span><br><span class="line">60</span><br><span class="line">61</span><br><span class="line">62</span><br><span class="line">63</span><br><span class="line">64</span><br><span class="line">65</span><br><span class="line">66</span><br><span class="line">67</span><br><span class="line">68</span><br><span class="line">69</span><br><span class="line">70</span><br><span class="line">71</span><br><span class="line">72</span><br></pre></td><td class="code"><pre><span class="line">注册观察者之前</span><br><span class="line">	one:&lt;Person: 0x60000002a8a0&gt;</span><br><span class="line">	表面的类: Person</span><br><span class="line">	真实类型: Person</span><br><span class="line">	方法列表: setUserName:,userName,.cxx_destruct,printInfo,observeValueForKeyPath:ofObject:change:context:,height,setHeight:,setAge:,age</span><br><span class="line">	方法列表2: setUserName:,userName,.cxx_destruct,printInfo,observeValueForKeyPath:ofObject:change:context:,height,setHeight:,setAge:,age</span><br><span class="line"></span><br><span class="line">	two:&lt;Person: 0x6000000296c0&gt;</span><br><span class="line">	表面的类: Person</span><br><span class="line">	真实类型: Person</span><br><span class="line">	方法列表: setUserName:,userName,.cxx_destruct,printInfo,observeValueForKeyPath:ofObject:change:context:,height,setHeight:,setAge:,age</span><br><span class="line">	方法列表2: setUserName:,userName,.cxx_destruct,printInfo,observeValueForKeyPath:ofObject:change:context:,height,setHeight:,setAge:,age</span><br><span class="line"></span><br><span class="line">	three:&lt;Person: 0x60000002fae0&gt;</span><br><span class="line">	表面的类: Person</span><br><span class="line">	真实类型: Person</span><br><span class="line">	方法列表: setUserName:,userName,.cxx_destruct,printInfo,observeValueForKeyPath:ofObject:change:context:,height,setHeight:,setAge:,age</span><br><span class="line">	方法列表2: setUserName:,userName,.cxx_destruct,printInfo,observeValueForKeyPath:ofObject:change:context:,height,setHeight:,setAge:,age</span><br><span class="line"></span><br><span class="line">one方法名setUserName:：Class=0x10f528710 subClass:0x10f528710</span><br><span class="line">two方法名setUserName:：Class=0x10f528710 subClass:0x10f528710</span><br><span class="line">three方法名setUserName:：Class=0x10f528710 subClass:0x10f528710</span><br><span class="line">注册观察者之后</span><br><span class="line">2018-03-26 11:00:57.025622+0800 iOSInterview[3214:356624]</span><br><span class="line">	父类：Person</span><br><span class="line">	one:&lt;Person: 0x60000002a8a0&gt;</span><br><span class="line">	表面的类: Person</span><br><span class="line">	真实类型: NSKVONotifying_Person</span><br><span class="line">	方法列表: setHeight:,setAge:,setUserName:,class,dealloc,_isKVOA</span><br><span class="line">	方法列表2: setUserName:,userName,.cxx_destruct,printInfo,observeValueForKeyPath:ofObject:change:context:,height,setHeight:,setAge:,age</span><br><span class="line"></span><br><span class="line">	two:&lt;Person: 0x6000000296c0&gt;</span><br><span class="line">	表面的类: Person</span><br><span class="line">	真实类型: NSKVONotifying_Person</span><br><span class="line">	方法列表: setHeight:,setAge:,setUserName:,class,dealloc,_isKVOA</span><br><span class="line">	方法列表2: setUserName:,userName,.cxx_destruct,printInfo,observeValueForKeyPath:ofObject:change:context:,height,setHeight:,setAge:,age</span><br><span class="line"></span><br><span class="line">	three:&lt;Person: 0x60000002fae0&gt;</span><br><span class="line">	表面的类: Person</span><br><span class="line">	真实类型: Person</span><br><span class="line">	方法列表: setUserName:,userName,.cxx_destruct,printInfo,observeValueForKeyPath:ofObject:change:context:,height,setHeight:,setAge:,age</span><br><span class="line">	方法列表2: setUserName:,userName,.cxx_destruct,printInfo,observeValueForKeyPath:ofObject:change:context:,height,setHeight:,setAge:,age</span><br><span class="line"></span><br><span class="line">one方法名setAge:：Class=0x10f528770 subClass:0x10f886106</span><br><span class="line">two方法名setAge:：Class=0x10f528770 subClass:0x10f886106</span><br><span class="line">three方法名setAge:：Class=0x10f528770 subClass:0x10f528770</span><br><span class="line">2018-03-26 11:00:57.026266+0800 iOSInterview[3214:356624] Person:&#123;</span><br><span class="line">    kind = 1;</span><br><span class="line">    new = 18;</span><br><span class="line">&#125;</span><br><span class="line">赋值观察者之后</span><br><span class="line">	one:&lt;Person: 0x60000002a8a0&gt;</span><br><span class="line">	表面的类: Person</span><br><span class="line">	真实类型: NSKVONotifying_Person</span><br><span class="line">	方法列表: setHeight:,setAge:,setUserName:,class,dealloc,_isKVOA</span><br><span class="line">	方法列表2: setUserName:,userName,.cxx_destruct,printInfo,observeValueForKeyPath:ofObject:change:context:,height,setHeight:,setAge:,age</span><br><span class="line"></span><br><span class="line">	two:&lt;Person: 0x6000000296c0&gt;</span><br><span class="line">	表面的类: Person</span><br><span class="line">	真实类型: NSKVONotifying_Person</span><br><span class="line">	方法列表: setHeight:,setAge:,setUserName:,class,dealloc,_isKVOA</span><br><span class="line">	方法列表2: setUserName:,userName,.cxx_destruct,printInfo,observeValueForKeyPath:ofObject:change:context:,height,setHeight:,setAge:,age</span><br><span class="line"></span><br><span class="line">	three:&lt;Person: 0x60000002fae0&gt;</span><br><span class="line">	表面的类: Person</span><br><span class="line">	真实类型: Person</span><br><span class="line">	方法列表: setUserName:,userName,.cxx_destruct,printInfo,observeValueForKeyPath:ofObject:change:context:,height,setHeight:,setAge:,age</span><br><span class="line">	方法列表2: setUserName:,userName,.cxx_destruct,printInfo,observeValueForKeyPath:ofObject:change:context:,height,setHeight:,setAge:,age</span><br><span class="line"></span><br><span class="line">one方法名setAge:：Class=0x10f528770 subClass:0x10f886106</span><br><span class="line">two方法名setAge:：Class=0x10f528770 subClass:0x10f886106</span><br><span class="line">three方法名setAge:：Class=0x10f528770 subClass:0x10f528770</span><br></pre></td></tr></table></figure>

<h4 id="总结："><a href="#总结：" class="headerlink" title="总结："></a>总结：</h4><p>1、在未添加观察者之前，运行时的类和对象本身的类是一样的。添加KVO后生成NSKVONotifying_Person类，打印NSKVONotifying_Person父类(superclass)为Person，表明<strong>NSKVONotifying_A</strong>为<strong>A</strong>的派生类。</p>
<p>2、打印方法列表，one,two<code>[obj class]</code>与<code>object_getClass(obj)</code>的方法列表不同，而没有监听属性的three一切正常。可以看到注册KVO后isa指针(<code>object_getClass(obj</code>)对象为NSKVONotifying_Person，并重写了了setHeight，setAge等setter方法,从而利用<code>willChangeValueForKey</code>与<code>didChangevlueForKey</code> 来激活键值通知机制。</p>
<p>Apple 使用了 isa 混写（isa-swizzling）来实现 KVO 。当观察对象A时，KVO机制动态创建一个新的名为：<strong>NSKVONotifying_A</strong> 的新类，该类继承自对象A的本类，且 KVO 为 <strong>NSKVONotifying_A</strong> 重写观察属性的 setter 方法，setter 方法会负责在调用原 setter 方法之前和之后，通知所有观察对象属性值的更改情况。</p>
<p>（备注： isa 混写（isa-swizzling）isa：is a kind of ； swizzling：混合，搅合；）</p>
<p>KVO 的键值观察通知依赖于 NSObject 的两个方法:<code>willChangeValueForKey</code>:和 <code>didChangevlueForKey</code>:，在存取数值的前后分别调用。</p>
<h4 id="参考文档"><a href="#参考文档" class="headerlink" title="参考文档"></a>参考文档</h4><p><a target="_blank" rel="noopener" href="https://developer.apple.com/library/content/documentation/Cocoa/Conceptual/KeyValueObserving/KeyValueObserving.html">https://developer.apple.com/library/content/documentation/Cocoa/Conceptual/KeyValueObserving/KeyValueObserving.html</a></p>
</div></article><div class="post-copyright"><div class="post-copyright__author"><span class="post-copyright-meta">文章作者: </span><span class="post-copyright-info"><a href="mailto:undefined">kyren</a></span></div><div class="post-copyright__type"><span class="post-copyright-meta">文章链接: </span><span class="post-copyright-info"><a href="http://huluo666.gitee.io/2018/03/22/KVO原理及实现/">http://huluo666.gitee.io/2018/03/22/KVO原理及实现/</a></span></div><div class="post-copyright__notice"><span class="post-copyright-meta">版权声明: </span><span class="post-copyright-info">本博客所有文章除特别声明外，均采用 <a target="_blank" rel="noopener" href="https://creativecommons.org/licenses/by-nc-sa/4.0/">CC BY-NC-SA 4.0</a> 许可协议。转载请注明来自 <a href="http://huluo666.gitee.io">Kyren's Blog</a>！</span></div></div><div class="post-meta__tag-list"></div><nav id="pagination"><div class="prev-post pull-left"><a href="/2018/03/23/iOS%E4%B8%ADClass%E7%9B%B8%E5%85%B3%E6%96%B9%E6%B3%95%E5%8C%BA%E5%88%AB/"><i class="fa fa-chevron-left">  </i><span>iOS中Class相关方法区别</span></a></div><div class="next-post pull-right"><a href="/2018/03/22/iOS%E9%80%86%E5%90%91%E5%B7%A5%E7%A8%8B/"><span>iOS逆向工程</span><i class="fa fa-chevron-right"></i></a></div></nav></div></div><footer><div class="layout" id="footer"><div class="copyright">&copy;2022 By kyren</div><div class="framework-info"><span>驱动 - </span><a target="_blank" rel="noopener" href="http://hexo.io"><span>Hexo</span></a><span class="footer-separator">|</span><span>主题 - </span><a target="_blank" rel="noopener" href="https://github.com/Molunerfinn/hexo-theme-melody"><span>Melody</span></a></div><div class="footer_custom_text">hitokoto</div><div class="busuanzi"><script async src="//busuanzi.ibruce.info/busuanzi/2.3/busuanzi.pure.mini.js"></script><span id="busuanzi_container_page_pv"><i class="fa fa-file"></i><span id="busuanzi_value_page_pv"></span><span></span></span></div></div></footer><i class="fa fa-arrow-up" id="go-up" aria-hidden="true"></i><script src="https://cdn.jsdelivr.net/npm/animejs@latest/lib/anime.min.js"></script><script src="https://cdn.jsdelivr.net/npm/jquery@latest/dist/jquery.min.js"></script><script src="https://cdn.jsdelivr.net/npm/@fancyapps/fancybox@latest/dist/jquery.fancybox.min.js"></script><script src="https://cdn.jsdelivr.net/npm/velocity-animate@latest/velocity.min.js"></script><script src="https://cdn.jsdelivr.net/npm/velocity-ui-pack@latest/velocity.ui.min.js"></script><script src="/js/utils.js?version=1.9.0"></script><script src="/js/fancybox.js?version=1.9.0"></script><script src="/js/sidebar.js?version=1.9.0"></script><script src="/js/copy.js?version=1.9.0"></script><script src="/js/fireworks.js?version=1.9.0"></script><script src="/js/transition.js?version=1.9.0"></script><script src="/js/scroll.js?version=1.9.0"></script><script src="/js/head.js?version=1.9.0"></script><script src="/js/search/local-search.js"></script><script>if(/Android|webOS|iPhone|iPod|iPad|BlackBerry/i.test(navigator.userAgent)) {
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